Heat pumps and engines of the Stirling and Vuilleumier variety consist of at least two working fluid spaces, usually cylinders, that are held at different temperatures. The working fluid is fully contained within the system and displaced between the spaces either by a piston in each of the cylinders or by one or more separate displacers. In all but the simplest designs, the working fluid passes through a regenerator each time the working fluid is transferred between the spaces, giving up or taking on heat that is stored in the regenerator, from the last cycle, thereby increasing the efficiency of the system. These devices are well known it the art and are described thoroughly in the book The Regenerator and the Stirling Engine, by Allan J. Organ, (Wiley; 1 edition, Mar. 14, 1997, 624 pages). These systems are usually designed with high cycle rates in mind, often in the range of 1200 revolutions or cycles per minute, and therefore have comparatively open passages for fluid flow in order to avoid frictional losses. This approach allows for a high number of power cycles in a short period of time, thereby causing a mechanism of a given size and heat input to pay its way as efficiently as practicable, with regard to the fuel cost, maintenance cost, and the initial construction cost. The continuous motion of the device is usually ensured by phasing the mechanical action within the two spaces, usually at nearly 90 degrees to each other and including a flywheel or other harmonic means of inertially bringing about the next cycle.
Increased systemic ‘dead volume’, as described in a paper by B. Kongtragool et al (B. Kongtragool, S. Wongwises/Renewable Energy 31 (2006) 345-359), limits the net work and efficiency of these systems by allowing a significant portion of the compression or expansion of the working fluid to occur in that systemic dead volume rather than specifically in the chamber, cylinder or heat transfer area that was designed to do useful work. A change in working fluid pressure taking place within the regenerator or other ducting of a Stirling or Vuilleumier cycle device, will cause a temperature change in that portion of the working fluid, but not allow that temperature change to be communicated to a heat exchanging head in order to do useful work during that particular cycle. While heat energy that changes the pressure of the working fluid in portions of the system other than at the open end of the active cylinder is not necessarily lost, it is not made useful during that particular cycle. The useful work performed during a particular cycle is proportional to the change in pressure within the total system as well as the proportion of the working fluid that is in contact with the heat transfer surface of the open end of the active cylinder. Devices of this variety are notoriously difficult to scale up into larger, more powerful devices because of the difficulty in predicting the loss in power and efficiency due to the increased dead volume and corresponding reduction in the percentage of working fluid that is in contact with the heat transfer area that can make use of the working fluid's temperature difference. Power densities and efficiencies of larger systems usually require increased complexity and cost in order to properly balance dead volume against the system's resistance to the flow of working fluid.
Materials used for the construction of heat pumps of this variety are chosen for their strength, durability and heat retention and conduction properties as well as their tendency to resist oxidation or otherwise react to the working fluid at the temperatures and pressures of any particular device. Solid conductors, heat sinks and regenerator materials range from stainless steel to cotton and are configured geometrically to transfer heat energy as advantageously as possible for a given configuration while minimizing resistance to the flow of working fluid. Regenerator materials are usually configured into wire matrices that allow for maximal contact of the working fluid with a heat retaining material that will withstand repeated cycling of temperature and flow direction. Stacked screens or other geometric matrices of stainless steel, wire, or pellets are commonly used with the intent of maximizing the heat transfer properties to and from the working fluid without excessively conducting heat between the elements of the regenerator. This is to avoid losses due to systemic longitudinal heat flow within the matrix.
The objects of the invention are as follows:
To produce more work per unit volume during each cycle of a Stirling or Vuilleumier cycle device.
To produce a device that is predictably scalable into larger, more powerful devices, without an unreasonable loss of power or efficiency.
To avoid wasting the power invested in the compression and expansion cycles of a Stirling or Vuilleumier cycle system by reducing the dead volume in various areas.
In particular, to reduce dead volume in the regenerator to zero, or nearly zero, by placing it within the displacer/regenerator space and causing interstitial spaces of the heat regenerating elements to be fully purged of the working fluid during certain portions of each cycle by collapsing the nesting elements together, thereby forcing all working fluid into the most advantageously conductive portion of the active cylinder at that particular phase and time. To reduce dead volume within the heat transfer areas by providing increased surface areas in each compression or expansion chamber that can be fully purged of the working fluid during each cycle by nesting tapered pins of the heated and cooling heads within tapered holes of the end plates of the displacer/regenerator stack.
To allow the end plates of the displacer/regenerator stack to remain in contact with the heated or cooling head while the device opens other areas of the system, thereby transferring heat to or from the end plates' surfaces, making the heating or cooling of the fluid more rapid during the next cycle.
To provide for the flexible timing of cycles and phases without requiring the continuous motion of a mechanical linkage that operates at a particular, predetermined frequency or phase angle. To provide for the timing of cycles and phases in a manner that allows for a dwell period during any particular time in the cycle, in order to allow useful work to be accomplished as fully as practicable before proceeding to the next phase of the cycle.
To provide for the timing of cycles and phases in a manner that allows for a dwell period during any particular time in the cycle, in order to allow the transfer of heat to or from the head, piston or regenerator elements, to be accomplished as fully as advantageous at any particular temperature, pressure, flow rate and cycle rate before proceeding to the next phase of the cycle.
To provide for the timing of cycles and phases in a manner that allows any given chamber to open or close as fully as advantageous before any other chamber begins to open or close. To provide for timing of cycles and phases that allows any given chamber to begin to open or close at the most advantageous time in any given cycle, based on an algorithm that optimizes the timing according to the temperature, pressure, flow rate, cycle rate and positions of various portions of the system, according to sensors in those areas.
To reduce fluid frictional losses by cycling at a rate no greater than necessary to accomplish the presently assigned task, thereby allowing the minimization of working fluid passageway cross sectional areas and their associated dead volumes, whether inside or outside the regenerator.
To provide for timing of cycles and phases without requiring the addition of dead volume to accommodate the timing mechanism.
To reduce mechanical friction and working fluid pressure losses by avoiding the penetration of the sealed system by mechanical shafts or linkages.
To reduce longitudinal heat conduction through the regenerator elements by interleaving the regenerator elements with insulating material of similar geometry.
To prevent eddy currents from forming within the regenerator matrix by purging all working fluid from the matrix during each cycle, thereby stopping the flow of the working fluid at least momentarily, during at least a portion of each cycle.
To allow the pressure changes in one, heated/driving system, to be communicated to, and used directly in, another similar driven/cooling system, in order to avoid losses associated with the transformation of energy to and from its various forms, such as thermal, electrical, mechanical and chemical.
To allow for multiple heat sources for the heating of the driving portion of the device, including solar thermal heating as well as electrical, gas or waste heat from a process, building or vehicle. To allow for alternative power sources for the mechanism drive, including self generated internal pressures, an electric motor or solenoid, or a separate heat engine that is also powered by solar thermal, natural gas or waste heat.
To allow waste heat from the warm side of both driving and driven cylinders to be reused for other purposes, such as water heating.
To allow for the connection of this system's data processing unit to the system control of an associated building or process, to better integrate all systems efficiently.
To allow for the operation of the system as a building heating unit by reversing the phase of the second, driven cylinder in relation to the first.
To allow for excess power to be used as mechanical power to generate electricity or pump liquid by driving a piston or pistons with the pressure from the driving cylinder.